Hormonesaremoleculesthatactassignalsfromonetypeofcellstoanother.Mosthormonesreachtheirtargetsvia the blood.

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Endocrinologiststreatdisorders of the [[pituitary]],includinggrowthdisorders;diseases of the [[thyroid]];diseases of the [[adrenal]] glands;diseasesof the [[ovary]] and [[testes]];and [[diabetes]], adisorderofinsulinsecretionorsensitivity.

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Allmulticellularorganisms need coordinating systems to regulate and integrate the function of cells. Two mechanisms perform this function in higher animals: the nervoussystemandtheendocrine system. The endocrine system acts through the release (generally into the blood) of chemical agents and is vital to the properdevelopment and function of organisms. As Hadley notes,<ref>{{cite book |author=Hadley, Mac E. |title=Endocrinology |publisher=Prentice Hall |location=Englewood Cliffs, N.J |year=2000 |pages= |edition=5th ed.|isbn=0-13-080356-1 |oclc= |doi= |accessdate=}}</ref> the integration of developmental events such as proliferation, growth, and differentiation (including [[histogenesis]] and[[organogenesis]])and the coordination of [[metabolism]], [[Respiration (physiology)|respiration]],excretion, movement, [[reproduction]], andsensoryperception depend on chemical cues, substances synthesised andsecretedbyspecializedcells.

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==Background==

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Endocrinology is concerned with the study of the biosynthesis, storage, chemistry, and physiological function of [[hormones]] and with the cells of the endocrine glands and tissues that secrete them.

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Asevolutiondrove theemergence of multicellularorganismsitbecamenecessary to develop “coordinating systems to regulate and integrate the function of differentiating cells” (Griffin and Ojeda 2000). Two mechanisms perform this function in higher animals, the nervous system and the endocrine system. Unlike the former, whichsendsandreceivesinformation via electrochemical signals, the endocrinesystemperforms its regulatory function through the detection, production and release (generally into thebloodstream)of chemical agents. Theproperfunctionofthissystem is vital to the properdevelopment of organisms.AsHadley(2000)notes,theintegrationofdevelopmentaleventssuch as proliferation, growth, differentiation (including histogenesis and organogenesis) and the coordination of metabolism, respiration, excretion,movement,reproductionandsensoryperception are dependant on “chemical cues, substances synthesised and secreted by thespecialisedcells within theanimal”.

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Theendocrinesystemconsists of severalglands,indifferentparts of the body, thatsecretehormonesdirectlyinto the bloodratherthan into aductsystem. Hormoneshavemanydifferentfunctionsandmodes of action;onehormonemayhaveseveraleffectsondifferenttargetorgans, and, conversely, onetargetorganmaybeaffected by morethanonehormone.

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Endocrinologyconcernsitselfwiththestudyoftheendocrinesystem, primarilythebiosynthesis, storage, chemistryandphysiologicalfunctionofthe‘chemicalcues’orhormones (atermcoinedin1902–from the Greek&#972;&#961;&#956;&#940;&#969;“Iexcite”or“Iarouse”(Chester-Jonesetal1987)) but also the cells of the endocrineglands and tissues that secretethem. Itisalsoimportanttoconsiderthemechanismof,andfactorscontrolling,hormonesecretion;themechanismsofhormoneactionandreceptorbinding;thepathophysiologyofendocrinesystemdysfunctionand the effectofexogenoussubstancesonnormalfunction.

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Intheoriginal1902definitionbyBaylissandStarling(see below), theyspecifiedthat, to be classified as a hormone, achemicalmustbeproducedbyanorgan,bereleased (insmallamounts)intotheblood,and be transported by the bloodtoadistantorgantoexertitsspecificfunction.This definition holds for most "classical" hormones, but there are also [[paracrine]] mechanisms (chemical communication between cells within a tissue or organ), autocrine signals (a chemical that acts on the samecell), and [[intracrine]] signals (a chemical that actswithin the same cell).<ref>{{citebook|author=NusseyS,WhiteheadS|title=Endocrinology:AnIntegratedApproach|year=2001|pages=|isbn=1-85996-252-1|oclc=|doi=|accessdate=|publisher=BiosScientificPubl.|location=Oxford}}</ref>A[[neuroendocrine]]signalisa"classical"hormonethatis released into the bloodbyaneurosecretoryneuron(seearticleon [[Neuroendocrinology]]).

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Thestudyofendocrinologyeffectivelybeganwith a study by Berthold (1849), largely ignored at the time, in which he noted that castrated cockerels failed to develop combs and wattles or exhibit overtly male behaviour. It was further noted that the replacementof testes back into the abdominal cavity of either the same bird or another castrated individual resulted in normal behavioural and morphological development. Bertholdconcluded, rathererroneously, that the testes secreted a substancethatconditioned the blood (since they could no longer be nervously enervated) that, in turn, acted upon the body of the cockerel. In fact, oneof two otherthings could have been true based on these data: that the testes modified or activated a constituent of the blood or that the testes removed an inhibitory factor from the blood. It was not proven that the testes released a substance that engenders male characteristics until it was shown that the extract of testes could replace their function in castrated animals. Pure, crystalline testosterone was isolated in 1935 by David et al.

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Hormonesactbybindingtospecific[[Receptor (biochemistry)|receptors]] in the targetorgan. As[[Étienne-Émile_Baulieu|Baulieu]]notes, a receptorhasatleast two basicconstituents:

Althoughmostof the relevant tissues and endocrine glands had been extensively identified and categorised by early anatomists (and, later, microscopists) a morehumouralapproachtounderstandingbiologicalfunctionanddiseasewas favoured by classical thinkers such as Aristotle, Hippocrates,Lucretius, Celsus and Galen according to Freeman et al (2001) and these theories held sway until the advent of germ theory, physiology and organ basis of pathology in the 19thCentury.

The endocrine system is comprised of several glands located in diverse areas of the body. Morphologically they are noteworthy because they secrete directly into the bloodstream rather than into a duct system. The hormones produced by these glands can have different functions and modes of actions. One hormone can have multiple effects and target organs and, likewise, one physiological event or target organ can be affected by more than one hormone.

In 1902 Bayliss and Starling performed an experiment in which they observed that acid instilled into the duodenum caused the pancreas to begin secretion, evenafterthey had removed all nervous contact between the two. They also discovered the same response could be engendered by injecting jejunal mucosa. This demonstrated that some other factor, one that is inherent in the mucosa, wascausing a physiological response, andnotthenervoussystemwhich, at the time, was thought to be the only means of bodily communication. They termed the substance responsible for this chemical reflex secretin and coined the term hormone for chemicals that act in this manner. As part of this definition they specified that a chemical must be produced by an organ; be released (in small amounts) into the bloodstream; be transported to a distant organ and exert its specific function in order to be classified as ahormone. Although this definition applies to almost all ‘classical’ hormones there also exists [[paracrine]] mechanisms(achemicalcommunication between neighbouring cells within a tissue or organ), autocrine signals (a chemical that acts on the same cell) and intracrine signals (a chemical that acts within the same cell) (Nussey and Whitehead, 2001). A neuroendocrinesignalis a type of ‘classical’hormoneandisreleasedinto the bloodstreambyaneurosecretorycelluponexcited by a nervoussignal.

Hormonesmediatetheireffectsbybindingtospecific and unique receptors in the targetorganororgans,althoughtheresponsefollowingsuch recognition varies commensurate with the wide array of differing hormone functions. As Baulieu (1990) notes,though,areceptorconsistsofatleasttwobasicconstituents,to wit, arecognitionsiteto which the hormonebindsandaneffector (or executive) site, whichprecipitatesthemodificationofcellularfunction;betweenthese two entities is a mechanism of transduction in which hormone binding induces allosteric modification that, inturn,produces the appropriate response.

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[[Peptidehormones]]andproteinhormonesconsistofthree(in the caseof[[thyrotropin-releasinghormone]])tomorethan200(in the case of [[follicle-stimulating hormone]]) aminoacidresiduesandcanhavemolecularweightsaslargeas30,000.Allhormonessecretedby the pituitaryglandarepeptidehormones, asare[[leptin]]fromadipocytes,[[ghrelin]]fromthestomach, and[[insulin]]from the [[pancreas]].

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Griffin and Ojeda (2000) identify three different classes of hormone based on their chemical composition:

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===Steroid===

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[[Steroid hormones]] are converted from their parent compound, [[cholesterol]]. Mammalian steroid hormones can be grouped into five groups by the receptors to which they bind: [[glucocorticoids]], [[mineralocorticoids]], [[androgens]], [[estrogens]], and [[progestagens]].

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===Amines===

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==History and key discoveries of endocrinology==

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Amines, such as norepinephrine, epinephrineanddopamine,arederivedsingleaminoacids, inthiscasetyrosine.Thyroidhormoneslike3,5,3’-triiodothyronine (T3) and3,5,3’,5’-tetraiodothyronine(thyroxine, T4)makeup a subset of thisclassastheyderive from the combination of twoiodinatedtyrosineaminoacidresidues.

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The study of endocrinology began in China. The Chinese were isolating sex and pituitary hormones from human urine and using them for medicinal purposes by 200 BC<ref>Temple, Robert. ''The Genius of China.''pp. 141, 142. ISBN 9781594772177.</ref>. They used many complex methods, such as sublimation. <ref>Temple, Robert.''TheGeniusofChina.''p. 142.ISBN9781594772177</ref>Eventually, when[[ArnoldAdolphBerthold|Berthold]]notedthatcastratedcockerels did not develop combs and wattles or exhibit overtly male behaviour, European endocrinology began (however, it should be noted that the Chinese anticipated the science by over 1500 years.) <ref>Berthold AA. ''Transplantation der Hoden ''Arch. Anat. Phsiol. Wiss. Med.'' 1849;16:42-6.</ref> He found that replacement of testes back into the abdominal cavity of the same bird or another castrated bird resulted in normal behavioural and morphological development, and he concluded (erroneously) thatthe testes secreted a substance that "conditioned" the blood that, in turn, acted on the body of the cockerel. In fact, one of two other things could have been true: that the testes modifiedoractivated a constituent of thebloodorthatthe testes removed an inhibitory factor from the blood. It was not proven that the testes released a substance that engenders male characteristics until it was shown that the extract of testes could replace their function in castrated animals. Pure, crystalline [[testosterone]] was isolated in 1935.<ref>David K, Dingemanse E, Freud J ''et al''. ''Uber krystallinisches mannliches Hormon aus Hoden (Testosteron) wirksamer als aus harn oder aus Cholesterin bereitetes Androsteron. ''HoppeSeylersZPhysiolChem''1935;233:281.</ref>

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===Peptide/Protein===

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Although most of the relevant tissues and endocrine glands had been identified by early anatomists, a more humoral approach to understanding biological function and disease was favoured by classical thinkers such as [[Aristotle]], [[Hippocrates]], [[Lucretius]], [[Aulus Cornelius Celsus|Celsus]], and [[Galen]], according to Freeman et al,<ref>{{cite journal |author=Freeman ER, Bloom DA, McGuire EJ |title=A brief history of testosterone |journal=J. Urol. |volume=165 |issue=2 |pages=371–3 |year=2001 |pmid=11176375 |doi=10.1097/00005392-200102000-00004 |url=}}</ref> and these theories held sway until the advent of [[germ theory of disease|germ theory]], physiology, and organ basis of pathology in the 19th century.

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Peptide and Protein hormone are comprised of between three (in the case of thryotropin-releasing hormone (glutamic acid–histidine–proline)) and over 200 (in the case of follicle-stimulating hormone) amino acid residues and can have molecular weights as large as 30,000.

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===Steroid===

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In medieval [[History of Iran|Persia]], [[Avicenna]] (980-1037) provided a detailed account on [[diabetes mellitus]] in ''[[The Canon of Medicine]]'' (c. 1025), "describing the abnormal appetite and the collapse of sexual functions and he documented the sweet taste of diabetic urine." Like [[Aretaeus of Cappadocia]] before him, Avicenna recognized a primary and secondary diabetes. He also described diabetic [[gangrene]], and treated diabetes using a mixture of [[lupin]]e, [[trigonella]] ([[fenugreek]]), and [[zedoary]] seed, which produces a considerable reduction in the excretion of sugar, a treatment which is still prescribed in modern times. Avicenna also "described diabetes insipidus very precisely for the first time", though it was later [[Johann Peter Frank]] (1745-1821) who first differentiated between diabetes mellitus and diabetes insipidus.<ref name=Nabipour>{{citation|journal=International Journal of Endocrinology and Metabolism|year=2003|volume=1|pages=43–45 [44–5]|title=Clinical Endocrinology in the Islamic Civilization in Iran|last=Nabipour|first=I.}}</ref>

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Steroid hormones are derivatives of cholesterol and are subdivided into those with an intact steroid nucleus (gonadal and adrenal steroids) and those with a broken steroid nucleus (Vitamin D).

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==Work==

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In the 12th century, [[Zayn al-Din al-Jurjani]], another [[Islamic medicine|Muslim physician]], provided the first description of [[Graves' disease]] after noting the association of [[goitre]] and [[exophthalmos]] in his ''Thesaurus of the Shah of Khwarazm'', the major medical dictionary of its time.<ref name=WNI>{{WhoNamedIt|synd|1517|Basedow's syndrome or disease}} - the history and naming of the disease</ref><ref>{{citation|journal=Lakartidningen|year=1983|date=August 10, 1983|volume=80|issue=32-33|title=Who was the man behind the syndrome: Ismail al-Jurjani, Testa, Flagani, Parry, Graves or Basedow? Use the term hyperthyreosis instead|last=Ljunggren|first=J. G.|pages=2902 |pmid=6355710 }}</ref> Al-Jurjani also established an association between goitre and [[palpitation]].<ref name=Nabipour/> The disease was later named after Irish doctor Robert James Graves,<ref>{{WhoNamedIt|doctor|695|Robert James Graves}}</ref> who described a case of goiter with exophthalmos in 1835. The German [[Karl Adolph von Basedow]] also independently reported the same constellation of symptoms in 1840, while earlier reports of the disease were also published by the Italians Giuseppe Flajani and Antonio Giuseppe Testa, in 1802 and 1810 respectively,<ref>{{WhoNamedIt|doctor|1471|Giuseppe Flajani}}</ref> and by the English physician Caleb Hillier Parry (a friend of [[Edward Jenner]]) in the late 18th century.<ref>{{cite journal |author=Hull G |title=Caleb Hillier Parry 1755-1822: a notable provincial physician |journal=Journal of the Royal Society of Medicine |volume=91 |issue=6 |pages=335–8 |year=1998 |pmid=9771526 |pmc=1296785 |doi= |url=}}</ref>

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The medical specialty of endocrinology involves the diagnostic evaluation of a wide variety of symptoms and variations, as well as the long-term management of disorders of deficiency or excess of one or more hormones.

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Thepracticeofendocrinologyislaboratory-oriented.Acharacteristicofendocrinologyis that thediagnosisandtreatmentofendocrinediseases are guided by [[laboratory]] tests to agreaterextentthanformostspecialties.Manydiseasesareinvestigatedthrough''excitation/stimulation''or ''inhibition/suppression'' testing.Thismightinvolveinjectionwithastimulatingagentto testthefunction of anendocrineorgan.Bloodisthensampledtoassessthe changes of the relevanthormonesor metabolites. Anendocrinologistneedsextensive knowledge of [[clinical chemistry]] and [[biochemistry]]tounderstandtheusesandlimitationsoftheinvestigations.

Asecondimportantaspectof the practiceofendocrinologyisdistinguishinghumanvariationfromdisease.Atypicalpatterns of physicaldevelopment and abnormaltestresultsmustbeassessedasindicativeofdiseaseornot. [[Diagnosticimaging]] of endocrineorgansmayreveal"spots,"termed [[incidentaloma]]s, which do not representdisease.

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VonMeringandMinkowskimade the observationin1889thatremovingthe[[pancreas]]surgicallyledtoan increase in [[blood sugar]], followed by a coma and eventual death—symptoms of [[diabetes mellitus]]. In 1922,Banting and Bestrealizedthathomogenizingthepancreasandinjectingthederivedextractreversed this condition.<ref>{{citejournal|author=Bliss M |title=J. J. R. Macleod and the discovery of insulin|journal=QJExpPhysiol|volume=74 |issue=2 |pages=87–96 |year=1989 |pmid=2657840 |doi= |url=}}</ref> The hormone responsible, [[insulin]], was not discovered until Frederick Sanger sequenced it in1953.

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Endocrinologyalsorequirescaringforthepersonaswellasthedisease. Mostendocrinedisordersare [[chronicdisease]]swarrantinglife-longmedicalcare. The mostcommonoftheseisdiabetesmellitus. Successfulcareofdiabetes and otherchronicdiseasesnecessitatesunderstandingthepatientat the personalandsociallevelaswellas the molecular, and the physician-patientrelationshipcan be animportanttherapeuticprocess.

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[[Neurohormone]]swerefirstidentifiedby[[OttoLoewi]]in1921.<ref>Loewi,O.''Uebertragbarkeitder Herznervenwirkung.''Pfluger'sArch.gesPhysiol.1921;189:239-42.</ref> He incubated a frog's heart (innervated with its [[vagusnerve]] attached)inasaline bath, and left in the solution for some time. The solutionwasthenusedtobathea non-innervated second heart. Ifthevagusnerve on the first heart was stimulated, negative [[inotropic]] (beat amplitude) and [[chronotropic]](beatrate)activitywereseeninboth hearts. This did not occur in either heart if the vagusnervewasstimulated.Thevagusnerve was adding something to the saline solution. The effect could be blocked using atropine, a known inhibitor to heart vagal nerve stimulation. Clearly, something was being secreted by the vagus nerve and affecting the heart.The"[[vagusstuff]]" (as Loewi called it) causing the [[myotropic]] effects was later identified to be [[acetylcholine]]and [[norepinephrine]]. Loewi won the Nobel Prize forhisdiscovery.

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Apartfrommanagingpatients,manyendocrinologistsareinvolved in [[clinicalscience]] and [[medicalresearch]], [[teaching]] and [[hospitalmanagement]].

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Recentworkinendocrinologyfocusesonthemolecular mechanisms responsible for triggering the effects of hormones. The first example of such work being done was in 1962 by [[Earl_Wilbur_Sutherland_Jr.|EarlSutherland]].Sutherland investigated whether hormones enter cells to evoke action, or stayed outside of cells. He studied norepinephrine, which acts on the liver to convert [[glycogen]]into [[glucose]] via the activation of the [[phosphorylase]] enzyme. He homogenized the liver into a membrane fraction and soluble fraction (phosphorylase is soluble), added norepinephrine to the membrane fraction, extracted its soluble products, and added them to the first soluble fraction. Phosphorylase activated, indicating that norepinephrine's target receptor was on the cell membrane, not located intracellularly. He later identified the compound as cyclic AMP ([[Cyclicadenosine monophosphate|cAMP]]) and with his discovery created the concept of second-messenger-mediated pathways. He, like Loewi, won the Nobel Prize for his groundbreaking work in endocrinology.<ref>{{cite journal |author=Sutherland EW |title=Studies on the mechanism of hormone action |journal=Science |volume=177 |issue=47 |pages=401–8 |year=1972 |pmid=4339614 |doi= 10.1126/science.177.4047.401|url=http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=4339614}}</ref>

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==Training==

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==Endocrinology as a profession==

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Endocrinologistsarespecialistsof [[internal medicine]] or [[pediatrics]]. Reproductive endocrinologists primarily deal with problems of fertility and menstrual function. Most qualify as an [[internist]], [[pediatrician]], or [[gynecologist]] for a few years before specialising, depending on the local training system. In the U.S.andCanada,trainingforboardcertificationininternalmedicine, pediatrics,orgynecologyaftermedicalschool is referredto as residency. Furtherformaltrainingtosubspecializein adult, [[pediatric endocrinology|pediatric]], or reproductive endocrinology is referred to as a fellowship. Typical training for a North American endocrinologist involves 4 years of college, 4 years of medical school, 3 years of residency, and 3years of fellowship.

An ''endocrinologist'' is a [[physician|doctor]] who specializes in treating disorders of the endocrine system, such as [[diabetes]], [[hyperthyroidism]], and many others (see list of diseases below).

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===Work===

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The medical specialty of endocrinology involves the diagnostic evaluation of a wide variety of symptoms and variations and the long-term management of disorders of deficiency or excess of one or more hormones.

+

+

The diagnosis and treatment of endocrine diseases are guided by [[laboratory]] tests to a greater extent than for most specialties. Many diseases are investigated through ''excitation/stimulation'' or ''inhibition/suppression'' testing. This might involve injection with a stimulating agent to test the function of an endocrine organ. Blood is then sampled to assess the changes of the relevant hormones or metabolites. An endocrinologist needs extensive knowledge of [[clinical chemistry]] and [[biochemistry]] to understand the uses and limitations of the investigations.

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A second important aspect of the practice of endocrinology is distinguishing human variation from disease. Atypical patterns of physical development and abnormal test results must be assessed as indicative of disease or not. [[Diagnostic imaging]] of endocrine organs may reveal incidental findings called [[incidentaloma]]s, which may or may not represent disease.

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Endocrinology involves caring for the person as well as the disease. Most endocrine disorders are [[chronic disease]]s that need life-long care. Some of the most common endocrine diseases include [[diabetes]] mellitus, [[hypothyroidism]] and the metabolic syndrome. Care of diabetes, obesity and other chronic diseases necessitates understanding the patient at the personal and social level as well as the molecular, and the physician–patient relationship can be an important therapeutic process.

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Apart from treating patients, many endocrinologists are involved in [[clinical science]] and [[medical research]], [[teaching]], and [[hospital management]].

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===Training===

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There are roughly 70,000 to 80,000 endocrinologists in the United States. Endocrinologists are specialists of [[internal medicine]] or [[pediatrics]]. Reproductive endocrinologists deal primarily with problems of [[fertility]] and menstrual function—often training first in obstetrics. Most qualify as an [[internist]], [[pediatrician]], or [[gynecologist]] for a few years before specializing, depending on the local training system. In the U.S. and Canada, training for board certification in internal medicine, [[pediatrics]], or [[gynecology]] after medical school is called residency. Further formal training to subspecialize in adult, [[pediatric endocrinology|pediatric]], or reproductive endocrinology is called a fellowship. Typical training for a North American endocrinologist involves 4 years of college, 4 years of medical school, 3 years of residency, and 3 years of fellowship. Adult endocrinologists are board certified by the [[American Board of Internal Medicine]] (ABIM) in Endocrinology, Diabetes and Metabolism.

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===Professional organizations===

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In North America the principal professional organizations of endocrinologists include The Endocrine Society,<ref>[http://www.endo-society.org Endo-society.org]</ref> the American Association of Clinical Endocrinologists,<ref>[http://www.aace.com AACE.com]</ref> the American Diabetes Association,<ref>[http://www.diabetes.org Diabetes.org]</ref> the Lawson Wilkins Pediatric Endocrine Society,<ref>[http://www.lwpes.org lwpes.org]</ref> and the American Thyroid Association.<ref>[http://www.thyroid.org Thyroid.org]</ref>

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In the United Kingdom, the Society for Endocrinology<ref>[http://www.endocrinology.org endocrinology.org]</ref> and the British Society for Paediatric Endocrinology and Diabetes<ref>[http://www.bsped.org.uk bsped.org.uk]</ref> are the main professional organisations. The European Society for Paediatric Endocrinology<ref>[http://www.eurospe.org Eurospe.org]</ref> is the largest international professional association dedicated solely to paediatric endocrinology. There are numerous similar associations around the world.

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==Patient education==

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Because endocrinology encompasses so many conditions and diseases, there are many organizations that provide education to patients and the public. [[The Hormone Foundation]] is the public education affiliate of [[The Endocrine Society]] and provides information on all endocrine-related conditions. Other educational organizations that focus on one or more endocrine-related conditions include the [[American Diabetes Association]], [[National Osteoporosis Foundation]], Human Growth Foundation, American Menopause Foundation, Inc., and Thyroid Foundation of America.

==Diseases==

==Diseases==

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Amongthehundredsofendocrinological diseases are :

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:Seemainarticleat''[[Endocrine diseases]]''

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*[[Adrenal]]disorders:

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Adiseasedue to a disorder of the endocrine system is often called a "hormone imbalance", but is technically known as an ''endocrinopathy'' or ''endocrinosis''.

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** [[Adrenal insufficiency]]

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*** [[Addison's disease]]

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*** [[Congenital adrenal hyperplasia]] (adrenogenital syndrome)

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*** [[Mineralocorticoid deficiency]]

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** [[Conn's syndrome]]

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** [[Cushing's syndrome]]

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** [[Pheochromocytoma]]

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** [[Adrenocortical carcinoma]]

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* [[Glucose]] homeostasis disorders:

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** [[Diabetes mellitus]]

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** [[Hypoglycemia]]

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*** [[Idiopathic hypoglycemia]]

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*** [[Insulinoma]]

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* Metabolic [[bone]] disease:

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** [[Osteoporosis]]

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** [[Osteitis deformans]] (Paget's disease of bone)

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** [[Rickets]] and [[osteomalacia]]

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* [[Pituitary gland]] disorders:

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** [[Diabetes insipidus]]

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** [[Hypopituitarism]] (or [[hypopituitarism|Panhypopituitarism]])

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** [[Pituitary tumour]]s

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*** [[Pituitary adenoma]]s

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*** [[Prolactinoma]] (or [[Hyperprolactinaemia]])

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*** [[Acromegaly]], [[gigantism]]

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*** [[Cushing's disease]]

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* [[Parathyroid gland]] disorders:

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** [[Primary hyperparathyroidism]]

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** [[Secondary hyperparathyroidism]]

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** [[Tertiary hyperparathyroidism]]

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** [[Hypoparathyroidism]]

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*** [[Pseudohypoparathyroidism]]

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* Sex hormone disorders:

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** [[Disorders of sexual differentiation]] or intersex disorders

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*** [[Hermaphroditism]]

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*** [[Gonadal dysgenesis]]

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*** [[Androgen insensitivity syndrome]]s

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** [[Hypogonadism]]

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*** [[Gonadotropin deficiency]]

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*** [[Kallmann syndrome]]

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*** [[Klinefelter syndrome]]

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*** [[Ovarian failure]]

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*** [[Testicular failure]]

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*** [[Turner syndrome]]

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** Disorders of [[Gender]]

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*** [[Gender identity disorder]]

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** Disorders of Puberty

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*** [[Delayed puberty]]

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*** [[Precocious puberty]]

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** Menstrual function or fertility disorders

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*** [[Amenorrhoea]]

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*** [[Polycystic ovary syndrome]]

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* [[Thyroid]] disorders:

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** [[Hyperthyroidism]] and [[Graves-Basedow disease]]

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** [[Hypothyroidism]]

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** [[Thyroiditis]]

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** [[Thyroid cancer]]

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* Tumors of the endocrine glands not mentioned elsewhere

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** [[Multiple endocrine neoplasia]]

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*** [[Multiple endocrine neoplasia type 1|MEN type 1]]

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*** [[Multiple endocrine neoplasia type 2a|MEN type 2a]]

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*** [[Multiple endocrine neoplasia type 2b|MEN type 2b]].

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** See also separate organs

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* [[Autoimmune polyendocrine syndrome]]s

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* [[Incidentaloma]] - an unexpected finding on diagnostic imaging, often of endocrine glands

Endocrinology (from Greekἔνδον, endon, "within"; κρῑνω, krīnō, "to separate"; and -λογία, -logia) is a branch of medicine dealing with disorder of the endocrine system and its specific secretions called hormones.

Contents

Hormones are molecules that act as signals from one type of cells to another. Most hormones reach their targets via the blood.

All multicellular organisms need coordinating systems to regulate and integrate the function of cells. Two mechanisms perform this function in higher animals: the nervous system and the endocrine system. The endocrine system acts through the release (generally into the blood) of chemical agents and is vital to the proper development and function of organisms. As Hadley notes,[1] the integration of developmental events such as proliferation, growth, and differentiation (including histogenesis and organogenesis) and the coordination of metabolism, respiration, excretion, movement, reproduction, and sensory perception depend on chemical cues, substances synthesised and secreted by specialized cells.

Endocrinology is concerned with the study of the biosynthesis, storage, chemistry, and physiological function of hormones and with the cells of the endocrine glands and tissues that secrete them.

The endocrine system consists of several glands, in different parts of the body, that secrete hormones directly into the blood rather than into a duct system. Hormones have many different functions and modes of action; one hormone may have several effects on different target organs, and, conversely, one target organ may be affected by more than one hormone.

In the original 1902 definition by Bayliss and Starling (see below), they specified that, to be classified as a hormone, a chemical must be produced by an organ, be released (in small amounts) into the blood, and be transported by the blood to a distant organ to exert its specific function. This definition holds for most "classical" hormones, but there are also paracrine mechanisms (chemical communication between cells within a tissue or organ), autocrine signals (a chemical that acts on the same cell), and intracrine signals (a chemical that acts within the same cell).[2] A neuroendocrine signal is a "classical" hormone that is released into the blood by a neurosecretory neuron (see article on Neuroendocrinology).

Hormones act by binding to specific receptors in the target organ. As Baulieu notes, a receptor has at least two basic constituents:

a recognition site, to which the hormone binds

an effector site, which precipitates the modification of cellular function.[3]

Between these is a "transduction mechanism" in which hormone binding induces allosteric modification that, in turn, produces the appropriate response.

Amines, such as norepinephrine, epinephrine, and dopamine, are derived from single amino acids, in this case tyrosine. Thyroid hormones such as 3,5,3’-triiodothyronine (T3) and 3,5,3’,5’-tetraiodothyronine (thyroxine, T4) make up a subset of this class because they derive from the combination of two iodinated tyrosine amino acid residues.

The study of endocrinology began in China. The Chinese were isolating sex and pituitary hormones from human urine and using them for medicinal purposes by 200 BC[5]. They used many complex methods, such as sublimation. [6] Eventually, when Berthold noted that castrated cockerels did not develop combs and wattles or exhibit overtly male behaviour, European endocrinology began (however, it should be noted that the Chinese anticipated the science by over 1500 years.) [7] He found that replacement of testes back into the abdominal cavity of the same bird or another castrated bird resulted in normal behavioural and morphological development, and he concluded (erroneously) that the testes secreted a substance that "conditioned" the blood that, in turn, acted on the body of the cockerel. In fact, one of two other things could have been true: that the testes modified or activated a constituent of the blood or that the testes removed an inhibitory factor from the blood. It was not proven that the testes released a substance that engenders male characteristics until it was shown that the extract of testes could replace their function in castrated animals. Pure, crystalline testosterone was isolated in 1935.[8]

Although most of the relevant tissues and endocrine glands had been identified by early anatomists, a more humoral approach to understanding biological function and disease was favoured by classical thinkers such as Aristotle, Hippocrates, Lucretius, Celsus, and Galen, according to Freeman et al,[9] and these theories held sway until the advent of germ theory, physiology, and organ basis of pathology in the 19th century.

In medieval Persia, Avicenna (980-1037) provided a detailed account on diabetes mellitus in The Canon of Medicine (c. 1025), "describing the abnormal appetite and the collapse of sexual functions and he documented the sweet taste of diabetic urine." Like Aretaeus of Cappadocia before him, Avicenna recognized a primary and secondary diabetes. He also described diabetic gangrene, and treated diabetes using a mixture of lupine, trigonella (fenugreek), and zedoary seed, which produces a considerable reduction in the excretion of sugar, a treatment which is still prescribed in modern times. Avicenna also "described diabetes insipidus very precisely for the first time", though it was later Johann Peter Frank (1745-1821) who first differentiated between diabetes mellitus and diabetes insipidus.[10]

In the 12th century, Zayn al-Din al-Jurjani, another Muslim physician, provided the first description of Graves' disease after noting the association of goitre and exophthalmos in his Thesaurus of the Shah of Khwarazm, the major medical dictionary of its time.[11][12] Al-Jurjani also established an association between goitre and palpitation.[10] The disease was later named after Irish doctor Robert James Graves,[13] who described a case of goiter with exophthalmos in 1835. The German Karl Adolph von Basedow also independently reported the same constellation of symptoms in 1840, while earlier reports of the disease were also published by the Italians Giuseppe Flajani and Antonio Giuseppe Testa, in 1802 and 1810 respectively,[14] and by the English physician Caleb Hillier Parry (a friend of Edward Jenner) in the late 18th century.[15]

In 1902 Bayliss and Starling performed an experiment in which they observed that acid instilled into the duodenum caused the pancreas to begin secretion, even after they had removed all nervous connections between the two.[16] The same response could be produced by injecting extract of jejunum mucosa into jugular vein, showing that some factor in the mucosa was responsible. They named this substance "secretin" and coined the term hormone for chemicals that act in this way.

Von Mering and Minkowski made the observation in 1889 that removing the pancreas surgically led to an increase in blood sugar, followed by a coma and eventual death—symptoms of diabetes mellitus. In 1922, Banting and Best realized that homogenizing the pancreas and injecting the derived extract reversed this condition.[17] The hormone responsible, insulin, was not discovered until Frederick Sanger sequenced it in 1953.

Neurohormones were first identified by Otto Loewi in 1921.[18] He incubated a frog's heart (innervated with its vagus nerve attached) in a saline bath, and left in the solution for some time. The solution was then used to bathe a non-innervated second heart. If the vagus nerve on the first heart was stimulated, negative inotropic (beat amplitude) and chronotropic (beat rate) activity were seen in both hearts. This did not occur in either heart if the vagus nerve was stimulated. The vagus nerve was adding something to the saline solution. The effect could be blocked using atropine, a known inhibitor to heart vagal nerve stimulation. Clearly, something was being secreted by the vagus nerve and affecting the heart. The "vagusstuff" (as Loewi called it) causing the myotropic effects was later identified to be acetylcholine and norepinephrine. Loewi won the Nobel Prize for his discovery.

Recent work in endocrinology focuses on the molecular mechanisms responsible for triggering the effects of hormones. The first example of such work being done was in 1962 by Earl Sutherland. Sutherland investigated whether hormones enter cells to evoke action, or stayed outside of cells. He studied norepinephrine, which acts on the liver to convert glycogen into glucose via the activation of the phosphorylase enzyme. He homogenized the liver into a membrane fraction and soluble fraction (phosphorylase is soluble), added norepinephrine to the membrane fraction, extracted its soluble products, and added them to the first soluble fraction. Phosphorylase activated, indicating that norepinephrine's target receptor was on the cell membrane, not located intracellularly. He later identified the compound as cyclic AMP (cAMP) and with his discovery created the concept of second-messenger-mediated pathways. He, like Loewi, won the Nobel Prize for his groundbreaking work in endocrinology.[19]

The medical specialty of endocrinology involves the diagnostic evaluation of a wide variety of symptoms and variations and the long-term management of disorders of deficiency or excess of one or more hormones.

The diagnosis and treatment of endocrine diseases are guided by laboratory tests to a greater extent than for most specialties. Many diseases are investigated through excitation/stimulation or inhibition/suppression testing. This might involve injection with a stimulating agent to test the function of an endocrine organ. Blood is then sampled to assess the changes of the relevant hormones or metabolites. An endocrinologist needs extensive knowledge of clinical chemistry and biochemistry to understand the uses and limitations of the investigations.

A second important aspect of the practice of endocrinology is distinguishing human variation from disease. Atypical patterns of physical development and abnormal test results must be assessed as indicative of disease or not. Diagnostic imaging of endocrine organs may reveal incidental findings called incidentalomas, which may or may not represent disease.

Endocrinology involves caring for the person as well as the disease. Most endocrine disorders are chronic diseases that need life-long care. Some of the most common endocrine diseases include diabetes mellitus, hypothyroidism and the metabolic syndrome. Care of diabetes, obesity and other chronic diseases necessitates understanding the patient at the personal and social level as well as the molecular, and the physician–patient relationship can be an important therapeutic process.

There are roughly 70,000 to 80,000 endocrinologists in the United States. Endocrinologists are specialists of internal medicine or pediatrics. Reproductive endocrinologists deal primarily with problems of fertility and menstrual function—often training first in obstetrics. Most qualify as an internist, pediatrician, or gynecologist for a few years before specializing, depending on the local training system. In the U.S. and Canada, training for board certification in internal medicine, pediatrics, or gynecology after medical school is called residency. Further formal training to subspecialize in adult, pediatric, or reproductive endocrinology is called a fellowship. Typical training for a North American endocrinologist involves 4 years of college, 4 years of medical school, 3 years of residency, and 3 years of fellowship. Adult endocrinologists are board certified by the American Board of Internal Medicine (ABIM) in Endocrinology, Diabetes and Metabolism.

In North America the principal professional organizations of endocrinologists include The Endocrine Society,[20] the American Association of Clinical Endocrinologists,[21] the American Diabetes Association,[22] the Lawson Wilkins Pediatric Endocrine Society,[23] and the American Thyroid Association.[24]

In the United Kingdom, the Society for Endocrinology[25] and the British Society for Paediatric Endocrinology and Diabetes[26] are the main professional organisations. The European Society for Paediatric Endocrinology[27] is the largest international professional association dedicated solely to paediatric endocrinology. There are numerous similar associations around the world.

Because endocrinology encompasses so many conditions and diseases, there are many organizations that provide education to patients and the public. The Hormone Foundation is the public education affiliate of The Endocrine Society and provides information on all endocrine-related conditions. Other educational organizations that focus on one or more endocrine-related conditions include the American Diabetes Association, National Osteoporosis Foundation, Human Growth Foundation, American Menopause Foundation, Inc., and Thyroid Foundation of America.